Prerequisits for the validation of exoplanets

the validation of the signal for a candidate for each detection method (radial velocity, transits, imaging etc)

in case of a validated signal, does it prove that a stellar companion is detected ?

in case the companion is validated, does it satisfy the convention on the "definition" of exoplanets ?

I will show that all these steps raise some problems, sometimes with no solution. I will also discuss the special configuration of "free-floatting" planets. Some pragmatic conclusions and suggestions will be drawn.

I will revise methods to derive the masses, ages and evolutionary status of planet-hosting stars, with emphasis on Bayesian methods that employ both the observed properties (photometry, parallaxes, spectroscopy, asteroseismology) and libraries of stellar evolutionary tracks. I will also describe the use (and reliability) of star count models to infer the likely properties of stellar populations observed by a survey.

Slides Girardi

Talk Girardi

Stellar and planetary evolution

by J. Leconte

Slides Leconte

Talk Leconte

The Besançon stellar population model of the Galaxy

by C. Reylé & A. Robin

The population synthesis approach aims at assembling together current scenarii of galaxy formation and evolution, theory of stellar formation and evolution, models of stellar atmospheres and dynamical constraints, in order to make a consistent picture explaining currently available observations of different types (photometry, astrometry, spectroscopy) at different wavelengths. In this presentation, I will review the most recent updates of the Besançon Galaxy model and show how it can be used in the framework of planet validation.

Slides Reylé

Talk Reylé

How planetary statistics and comparisons of theory and observation can assist planet validation

by C. Mordasini, H. Klahr, Y. Alibert, T. Henning & W. Benz

While planet validation is primarily an observational task, there are a number of approaches how planet formation and evolution theory can assist this process. In my talk, I will first give an overview of important planetary statistics and comparisons of theory and observation. I will then address how such studies can assist planet validation for different observational techniques. This includes classical tests of orbital stability with N-body simulations but also the identification of observed mass-radius or mass-luminosity values for a planet candidate that are "impossible" according to theoretical models which, of course, can be incorrect. Finally, one can also ask how likely it is that a planet candidate of given observed properties is real based on theoretical and observational statistical considerations. I will end by discussing the opportunities and limitations of such an approach.

Slides Mordasini

Talk Mordasini

The Mass of KOI-94d and a Relation for Planet Radius, Mass, and Incident Flux

We measure the mass of a modestly irradiated giant planet, KOI-94d. We wish to determine whether this planet, which is in a 22-day orbit and receives 2700 times as much incident flux as Jupiter, is as dense as Jupiter or rarefied like inflated hot Jupiters. KOI-94 also hosts 3 smaller transiting planets, all of which were detected by the Kepler Mission. With 26 radial velocities of KOI-94 from the W. M. Keck Observatory and a simultaneous fit to the Kepler light curve, we measure the mass of the giant planet (106 +/- 11 M_E) and determine that it is not inflated. Support for the planetary interpretation of the other three candidates comes from gravitational interactions through transit timing variations, the statistical robustness of multi-planet systems against false positives, and several lines of evidence that no other star resides within the photometric aperture, including adaptive optics imaging, speckle imaging, spectral analysis, and dynamic analysis. The radial velocity analyses of KOI-94b and KOI-94e offer marginal (>2 sigma) mass detections, whereas the observations of KOI-94c offer only an upper limit to its mass. Using the KOI-94 system and other planets with published values for both mass and radius (138 exoplanets total, including 35 with M < 150 Earth masses), we establish two fundamental planes for exoplanets that relate their mass, incident flux, and radius from a few Earth masses up to ten Jupiter masses. These equations can be used to predict the radius or mass of a planet.

Slides Weiss

Talk Weiss

Multiple systems as a source of false positives in exoplanet detections

by A. Tokovinin & J.-L. Halbwachs

Multiple systems may be erroneously taken as exoplanetary host stars when they include faint close binary stars. A large sample of F-G type unevolved stars nearer than 67 pc is used to derive the distributions of periods and mass ratios for different hierarchical levels of multiple systems. A rough estimation of the rate of systems potentially generating false exoplanet detections is derived.

Slides Tokovinin

Statistical comparison of models

by P. Bordé

Slides Bordé

Validation of Transiting Planet Candidates with BLENDER

by W. Torres & F. Fressin

I will provide a brief description of the main philosophy behind the BLENDER algorithm that has been used by the Kepler Project to statistically ""validate"" candidate transiting planets. I will discuss also how the observational constraints are incorporated into the process, including high-resolution imaging, high-resolution spectroscopy, color information, and an analysis of the centroid motion of the target. I will also describe the procedures that have been applied to compute the blend frequencies for different false positive configurations, and to establish the ""planet prior"", particularly in some of the most difficult cases.

Slides Torres

Talk Torres

Planet Analysis and Small Transit Investigation Software

by R. Diaz, J.-M. Almenara, A. Santerne & C. Moutou

The majority of the smallest transiting planet candidates detected by the space missions CoRoT and Kepler cannot be directly confirmed by a dynamical measurement of their mass. This is due mainly to the faintness of the typical stars observed and to the small reflex motion induced by low-mass planets on their host stars. A way out of this problem is to statistically validate these candidates. In this talk, I will present PASTIS, the planet validation tool developed in Marseille. PASTIS aims at providing a rigorous and fast method to validate a large number of planet candidates. I will describe in detail most of the elements constituting PASTIS, and I will discuss the simulations performed to investigate the capabilities and limitations of our approach.

Most transit signals detected by Corot and other transit surveys are not due to exoplanets, but rather to stellar companions. A large fraction of these transits can be readily classified as non-exoplanetary in nature by a series of simple tests using quantities measured from the lightcurves, together with information about the target star environments. In the cases where the natures of the transiting bodies cannot be established, the test results can still be used to make informed choices for follow-up observations. In this talk, I will describe the procedure I use for the classification of exoplanet transit candidates in Corot data, and discuss a few examples.

Slides Bordé

Validating the planet sample from the Kepler pipeline

In order to understand the planet sample being produced by the Kepler pipeline, we need to know both the reliability (the false positive rate) and the completeness (the false negative rate) of the sample. We present the results of the first direct measurement of the completeness of the Kepler pipeline. This is measured by the injection and recovery of simulated planet transits into the pixel-level data and subsequent analysis through the standard Kepler pipeline. We also discuss how experiments like this can inform and improve BLENDER-style planet candidate validation, by constraining the parameter space in which the Kepler pipeline is able to discriminate between true planet candidates and astrophysical false positives.

Slides Christiansen

Talk Christiansen

Can we hope to validate the smallest planet candidates from Kepler ?

by T. Barclay

Kepler is succeeding in finding smaller planets on longer orbital periods. We are now at a stage where we have a significant numbers of Earth-sized planet candidates in the habitable zones around their host stars. I show what observations are necessary for their validation as bona fide planets.

Planet validation in radial velocity

Planet validation in astrometry

by A. Sozzetti

TBD

Talk Sozzetti

Astrophysical false alarms in high contrast imaging surveys

by G. Chauvin

After summarizing the main lessons learned from past imaging studies, I will review the main sources of contamination in deep imaging surveys aimed at searching for exoplanets and brown dwarfs companions. I will consider the specific work done for the preparation of the SPHERE/NIRSUR exoplanet survey of 200 nights. It illustrates how this information can be considered to optimize the survey strategy in terms of follow-up observations, astrophysical false alarm rejection and final characterization for planet validation.

Slides Chauvin

Talk Chauvin

Astrophysical false positives in direct imaging for exoplanets : a white dwarf close to a rejuvenated star

As is the case for all techniques involved in the research for exoplanets, direct imaging has to take into account the probability of so-called astrophysical false positives, which are phenomena that mimic the signature of objects we are seeking. In this work we aim to present a case of a false positive found during a direct imaging survey conducted with VLT/NACO. A promising exoplanet candidate was detected around the K2-type star HD 8049 in July 2010. Its contrast of Delta_H = 7.05 at 1.57 arcsec allowed us to guess the presence of a 35 MJup companion at 50 projected AU, for the nominal system age and heliocentric distance. To check whether it was gravitationally bound to the host star, as opposed to an unrelated background object, we re-observed the system one year later and concluded a high probability of a bound system. We also used radial velocity measurements of the host star, spanning a time range of 30 yr, to constrain the companion’s mass and orbital properties, as well as to probe the host star’s spectral age indicators and general spectral energy distribution. We also obtained for the companion U-band imaging with EFOSC and NIR spectroscopy of the companion with SINFONI. Combining all these information we conclude that the companion of HD 8049 is a white dwarf (WD), with temperature Teff = 18800 ± 2100 K and mass M_WD = 0.56 ± 0.08 M_sun. The significant radial velocity trend coupled with the imaging data indicate that the most probable orbit has a semimajor axis of about 50 AU. The discrepancy between the age indicators suggested against a bona-fide young star. The moderately large level of chromospheric activity and fast rotation, mimicking the properties of a young star, might be induced by the exchange of mass with the progenitor of the WD. This example demonstrates some of the challenges in determining accurate age estimates and identifications of faint companions.

Slides Zurlo

Talk Zurlo

Microlensing planet detection and physical parameters determination

by A. Cassan & P. Fouqué

Galactic gravitational microlensing is a powerful method to detect extrasolar planets at large orbital distances from their stars, from giant planets down to Earth-mass planets. In this talk, we will review the properties of microlensing exoplanet discoveries, and then discuss the principle of planet validation on the basis of observational strategy and model parameter determination.

The effect of stellar spots on the transit timing variations as a planet validation method

by M. Oshagh, N. Santos, I. Boisse & A. Santerne

Stellar spots can cause difficulties in the detection of exoplanets and on the determination of precise planetary parameters through spectroscopic and photometric observations. For example, the overlap of a transiting planet and stellar spots can produce anomalies in the transit light curves. These anomalies may cause offsets in the transit timing measurements which lead to the false positive detection of non-transiting planets by transit timing variation (TTV) method. In this study, we carried out a quantitative analysis of the effects that stellar spots have on high precision transit light curves. Depending on the spot sizes and their distribution, anomalies can produce a TTV signal with an amplitude of the order of 200 seconds for typical sun-like spots. This amplitude can be attributed to the transit timing variation amplitude produced either by an Earth like planet on a Jovian planet in mean motion resonance, or by an Earth mass exomoon on the Neptune sized transiting planet.

Slides Oshagh

Transit light curves and stellar spots

by Sz. Csizmadia

Transiting exoplanets are key objects to measure the radii of exoplanets. The radius will give the most valuable extra information to our knowledge on exoplanets from transits, because it allows us to study the internal structure, atmosphere, surface inhomogeneties etc. of the planet. However, this require high precision (1-5% for internal structure studies) or extreme high accuracy (0.1% for atmospheric studies). The planet parameter determination is affected by several factors, like our knowledge on limb darkening, stellar activity, and the interaction between stellar activity and limb darkening. Furthermore, the stellar activity also has impact on the stellar radius measurements what introduces systematic errors. The list and the rate of these disturbing effects are summarized in this talk. Stellar spots also affects the measured TTVs. We also present ideas how to increase the accuracy in the transit parameter determination.

Slides Csizmadia

Talk Csizmadia

Transit Timing Variations and Dynamical Simulations as a tool for planet validation in multiple planet systems

by S. Hoyer, P. Rojo & M. Lopez-Morales

In the last years the Transit Timing Variations (TTVs) technique have been largely used to search for companions of transiting exoplanets. While Hot Jupiters do not present evidence of unseen companions via TTVs, Kepler data has revealed a large number of systems of less massive planets with clear TTV signals. Nowadays TTVs has became a main tool to detect and detect exoplanets among Kepler data when no other technique such as RVs can be applied. But the ’inverse problem’ (determination of physical parameters of the exoplanets based on the TTVs) is not straightforward and in some cases possibly highly degenerated. Despite different approaches to solve this problem have been proposed, the N-body simulations remain to be one of the most reliable solution. For our Transit Monitoring Program (TraMoS) we have developed an efficient pipeline where we can run a large number of dynamical simulations (Mercury code) that allows to us to sweep a wide range of values in the parameter space of our sample of 30+ transiting planets we currently monitor. With this N-body simulations we can prove the stability and the orbital and physical configuration of the planetary system based on the timing information. Here will present some results we have published where we have imposed strict constrains in the mass of hypothetical companions of Hot Jupiters based on their timing information and also we present other examples of information/applications we can extract from the dynamical simulations.

Slides Hoyer

Talk Hoyer

YETI - search for young transiting planets

So far, only transiting exoplanets older than several hundred Myr are known. To close the gap at young ages, the YETI network (Young Exoplanet Transit Initiative) was established. It consists of ground based telescopes with mirror sizes of 0.4 to 2m, located at different longitudes all over the world. We are able to observe continuously without gaps in the light curves and therefor not missing a transit.
The targets are young clusters, which provide a large number of young stars with similar properties. The first target was Trumpler 37 with an age of 4 Myr. Data processing of 50,000 images from 12 telescopes is still in progress, but we found already 2 transiting candidates, for which follow up was partly done. The first candidate turned out to be a binary star with late-type companion, while for the second candidate observation for radial velocity have still to be done. We are also monitoring 25 Ori (7 Myr), IC 348 (2 Myr), Col 69 (5 Myr) and NGC 1980 (5 Myr) in the YETI consortium. The analysis is still in progress, but a transiting candidate was recently reported in 25 Ori (van Eyken et al. 2012, ApJ 755, 42). The host star is an active T Tauri star, hence the activity variation overlap the radial velocity signal caused be the planet. We have to consider alternative planet validation methods to test planet candidates around stars with transit-like light curves which are fainter than some 16 mag in the optical. During our monitoring, we expect also more transit like signals at active T tauri stars, where the mass has to be measured.